Centrifugal blowers are designed to move quantities of air by raising the pressure of the air and discharging it at a desired volumetric flow rate through a pipe or duct. An apparatus requiring cooling, ventilation, or pressurization is often positioned at the discharge port of the pipe or duct. In order for the air to move at a continuous volumetric flow rate through the discharge port to cool, ventilate, or pressurize the apparatus, the air must be supplied with sufficient energy to overcome the downstream backpressure at the outlet. This backpressure is the sum of the pressure drop in the downstream system caused by the resistance of the air moving through the duct and the total air pressure at the discharge port. Oftentimes the downstream system has at least two separate branches through which air must be delivered to a corresponding number of components that require cooling, ventilation, or pressurization. These systems typically include blowers having two or more separate impellers wherein each impeller supplies air at a volumetric flow rate specific to the apparatus connected to its respective discharge port.
Such systems are incorporated into electric-drive off-road mining trucks and various other earth-moving devices, railroad locomotives, and marine vessels. One such mining truck is the KMS 930E provided by Komatsu Mining Systems (www.komatsumining.com). The drive system for such trucks includes a diesel-driven alternator that provides electrical power through a control group to AC drive motors connected to the wheels of the truck. A significant amount of heat is generated during the operation of the AC drive motors. This heat is removed from the drive motors by a supply of cooling air.
It is known to provide cooling air for such mining vehicles from a centrifugal blower connected directly to the drive shaft of the alternator. U.S. Pat. No. 4,448,573 describes a multiple outlet centrifugal blower for such applications. The blower casing includes two outlets that are displaced from one another so as to provide two independent flows of cooling air. One of the airflows is directed to cool the alternator and the other is directed to cool the drive motors. The arcuate extent of the respective outlet openings around the periphery of the impeller may be selected to control the pressure and volume flow rate of the respective airflows. In this type of blower, the total velocity head generated by the impeller blades at the respective arcuate position is used to drive the airflow into the respective outlet.
In addition to removing heat from the alternator and the drive motors, heat must also be removed from the electrical control group components of an electric-drive vehicle. In modern large mining vehicles, the airflow from the alternator shaft blower is dedicated to cooling the alternator. Cooling air for the drive motors and the control group is provided from two respective impellers situated on a single double-ended auxiliary blower unit. Air moved by the first impeller is ducted to the rear of the vehicle where it is used to cool the AC drive motors located inside the rear wheels of the truck. Air moved by the second impeller is ducted to the deck of the vehicle and is used to cool electrical components associated with the control group of the vehicle. The auxiliary blower unit is driven by an auxiliary AC drive motor, which is powered by an auxiliary inverter connected to the alternator. Such an independent dual-impeller ventilation system offers the benefit of providing independent cooling air flows to the alternator, control group and drive motors. However, such a configuration is mechanically complex and costly to build and to maintain.
What is needed is a ventilation system for an electric drive vehicle that eliminates the auxiliary blower unit yet still provides an independent cooling air flow for each of the alternator, control group and drive motors.